Background: Parental suicide attempts (SAs) and suicide death (SD) increase offspring risk for suicidal ideation (SI) and SAs. High levels of impulsivity have been observed in clinical samples of families vulnerable to suicide. Impulsivity is a highly heritable trait that is especially elevated in childhood. Of the five UPPS impulsivity facets, negative urgency has been consistently associated with SI and SA in adult studies. Our study examined the prospective association between the UPPS facets and onset of SI and SA in childhood, and their role as mediators of the association between parental SA/SD and offspring onset of SI and SA. Methods: The sample was 9,077 children (47.4% female, 9-to-10 years old) from the Adolescent Brain Cognitive Development (ABCD) study, assessed yearly three times. Only children with a biological parent as informants were included. At Time 1 (T1), parents reported on family history of SA/SD. Parents and children reported on lifetime SI and SA in the KSADS-5 at T1 and T3 (only child report at T2). UPPS-brief (child report) was used to assess the impulsivity facets at T1: sensation seeking, lack of premeditation, lack of perseverance, negative urgency, and positive urgency. UPPS facets were included as latent variables. Weighted SEM and causal mediation models were run in MPlus. Results: A T1, 5.6% children had a parent with SA or SD. At T2/T3, 9.1% children reported first-time SI (never SA) and 1.6% first-time SA. In unadjusted models, parental SA/SD was associated with first-time SI, first-time SA, and all facets, except sensation seeking. When covariates were included, parental SA/SD remained associated with negative and positive urgency and first-time SI. In mediation models testing one UPPS facet at a time, parental SA/SD had an indirect effect on first-time SI through negative urgency (B = 0.006, 95% CI, 0.002-0.01) and positive urgency (B = 0.004, 95% CI, 0.002-0.005). In models adjusted for sex, parental SA/SD had an indirect effect on first-time SA through negative urgency (B = 0.006, 95% CI, 0.003-0.013) Discussion: Our findings support an impulsivity pathway in the familial transmission of suicide risk. In offspring whose parents have attempted or died by suicide, clinicians should pay attention to children who impulsively act on negative and positive feelings, as they may be at higher risk for SI or SA.